This invention relates to a method of wiring a printed circuit board and particularly to a method of wiring a printed circuit board suitable for high-density and fine wiring.
In accordance with a recent trend toward an increase in the density and fineness of a printed circuit board, various proposals have been made in order to attain this purpose. One of the proposals is a method which comprises masking a copper clad laminate as a starting material at the portion other than the portion to be wired with a photoresist for plating and subjecting only the portion to be wire to plating, e.g., electroless copper plating for wiring. In this method, the resist for plating and metallic layer portion unnecessary for wiring (i.e., the metallic layer portion below the resist for plating) is removed after the completion of copper plating of the portion to be wired
However, the adhesion between the copper clad laminate and the photoresist for plating is generally poor, which raises a problem that it is impossible to conduct satisfactory wiring because the resist for plating is peeled off during plating. In particular, when fine wiring is intended, the occurrence of the peeling is a serious problem. In order to solve this problem, for example, Japanese Patent Laid-Open No. 48831/1986 has proposed a method which comprises mechanically rubbing the surface of a copper clad laminate etc. with pumice, applying an adhesion promoting agent, such as benzotriazole, to the rubbed surface, and masking the desired portion with a photoresist for plating. This method is one which has given a solution to the problem that the resist for plating is peeled from the surface of the undercoat copper layer during plating. Further, a method in which the same effect can be attained by adding an adhesion promoting agent such as benzotriazole to a photoresist for plating, has been proposed and has made it possible to solve the problem of the above-described peeling.
However, the use of benzotriazole or the like as the adhesion promoting agent in the above-described conventional techniques may have an adverse effect on the plating film. Specifically, in some cases, there have been arisen problems such as a lowering in the physical properties of the plating film, a lowering in the plating rate, and an uneven plating thickness, by the slight dissolving of the benzotriazole into the plating solution. The substance which has such an adverse effect is not limited to benzotriazole alone, and many similar compounds which are considered to serve as an adhesion promoting agent, e.g., heterocyclic compounds, such as 2-mercapto-benzothiazole, have a similar adverse effect. The occurrence of this problem makes it difficult to form a pattern with excellent reliability and, in some cases, makes pattern formation itself impossible.